Diabetes and its treatment with insulin in the rat result in dramatic changes in insulin-stimulated glucose transport activity and glucose transporter number in adipose cells. To understand the molecular basis for these changes, we have used the Hep G2 glucose transporter cDNA to assess glucose transporter mRNA transcripts by Northern blotting. The data suggest that 1) glucose transporter number in adipose cells from diabetic rats is not determined by glucose transporter mRNA levels whereas with insulin treatment increased glucose transporter mRNA may be responsible for increased glucose transporter number or 2) the Hep G2 glucose transporter cDNA detects an mRNA which does not encode the major insulin- responsive glucose transporter. Evidence has recently accumulated for a direct role of glucose, independent of insulin, in the regulation of cellular glucose transport. Moreover, we have demonstrated the reversal of in vivo insulin resistance in diabetic rats by normalization of hyperglycemia without any change in plasma insulin concentration. In the present study, the effect of correction of hyperglycemia on insulin's stimulatory action on glucose transport activity in adipose cells from diabetic rats has been examined. The data show that normalization of the plasma concentration in the absence of insulin therapy in diabetic rats restores, or may even enhance, the in vivo adipose cell glucose transport response to insulin while normalizing in vivo insulin- mediated glucose disposal and suggest that the plasma glucose concentration is an important regulator of glucose transport activity in adipose cells, independent of the plasma insulin concentration.